This invention relates in general to the charging of superconducting magnet coils and, more specifically, to a method and apparatus for charging superconducting magnet coils using thermocouple junctions in accordance with the Seebeck effect.
Superconducting magnets are coming into widespread use in particle accelerators for physics research and medical applications, as energy storage devices, to provide energy for systems such as magnetically levitated trains, etc. These superconducting magnets use coils of superconducting wire cooled below the critical temperature of the wire material, at which point the wire is essentially without electrical resistance. With present superconducting materials such as niobium-titanium alloys, the coils must be cooled with liquid helium, while the so-called high temperature superconductors such as YBa.sub.2 Cu.sub.3 O.sub.7 have higher critical temperatures, allowing cooling with liquid nitrogen.
Presently, such coils are electrically charged using large, heavy, power supplies and large switching systems. While these systems are very effective in charging very large, fixed, magnets such as the Superconducting Supercollider dipole magnets, they are undesirable for use in mobile systems, such as those used with magnetically levitated trains or space applications where the cost of launching the additional weight of a charging system is prohibitive.
Present charging systems require heavy leads penetrating into the magnet cooling system to charge the magnet. After charging, during magnet operation, these leads are a source of significant heat transfer into the cooling system, causing an undesirably large loss of the coolant liquid due to increased boil-off.
In past applications of thermoelectric power generation the low voltage potentials have been a disadvantage in many applications. The typical low voltage, high current characteristics of thermoelectricity is much better suited to the near zero resistance of superconducting magnets.
Thus, there is a continuing need for improved methods for charging superconducting magnet coils, especially for use in mobile or space magnet applications.